Calibrated thermostatic switch and method for calibrating the same including welded lug and recess means



Jan. 2, 1968 T. BRASSARD, JR. ET AL 3,361,883

CALIBRATED THERMOSTATIC SWITCH AND METHOD FOR CALIBRATING THE SAMEINCLUDING WELDED LUG AND RECESS MEANS 2 Sheets-Sheet 1 Original FiledFeb. 3, 1964 In wzztons; Tieeadore ,Brassard, Jr, Lawrence oqper,

Witness imam) WW 721] 9% 'Atgy.

3,361,883 IBRATING NS Jan. 2, 1968 T. BRASSARD, JR. E L

CALIBRATED THERMOSTATIC SWITCH AND METHOD FOR CAL THE SAME INCLUDINGWELDED LUG AND RECESS MEA Feb. 3, 1964 2 Sheets-Sheet 2 Original Filed Lm W 5 a/nifmz In were tons.- Theodore Brassari J21, Lawrerzcezf 6' er, aW

A My.

United States Patent 3,361,883 CALIBRATED THERMQSTATEC SWITCH AND METHODFOR CALKBRATING THE SAME INCLUDING WELDED LUG AND RECESS MEANS TheodoreBrassard, Jr., 5. Main St, RED. 1, Berkley, Mass., and Lawrence E.Cooper, Thayer Farm Road, RED. 1, Attleboro, Mass. 02703 Continuation ofapplication Ser. No. 341,881, Feb. 3, 1964. This application Nov. 1,1966, Ser. No. 591,336 6 Claims. (Cl. 2%0-122) ABSTRACT OF THEDTSCLOSURE A thermostatic switch adapted for miniaturization is shown tocomprise a base, first and second electrically conductive terminalsmounted on said base in electricallyinsulated relation to each other, astationary contact provided by a portion of said first terminal, amounting arm having first and second intersecting portions and havingsaid first arm portion secured to said base in electricallyinsulatingrelation to said terminals to dispose said second arm portion in spacedrelation to said base, a snap-acting thermostatic member electricallyconnected to the second terminal and having a deformed portionresponsible for its snap-action, an electrical contact supported on oneend of the thermostatic element for movement into and out of engagementwith the stationary contact in response to snap movement of thethermostatic member, and a welding lug secured to the opposite end ofthe thermostatic member so that an end of the lug extends from thethermostatic member. The second portion of the mounting arm has adish-shaped recess therein forming a locating surface and the extendingend of the welding lug fits into the mounting arm recess to engage thelocating surface, the lug being disposed in selected angular relation tothe mounting arm and being welded to the arm within the recess forsupporting the thermostatic member in spaced, cantilever relation to themounting arm in selected orientation relative to the stationary contactto calibrate the switch.

This application is a continuation of the copending application Ser. No.341,881, which was filed Feb. 3, 1964, and which is now abandoned.

This invention relates to thermostatic switches, and in particular, tothermostatic switches of the snap-acting type which are small enough tobe inserted or embedded directly in the windings of small, fractionalhorsepower motors or into cavities of small motors and smalltransformers, the thermostatic switch serving to prevent such devicesfrom overheating. It is to be understood, however, that the invention isnot limited to such protective use mentioned above but may be usedwherever found applicable.

It is one object of the instant invention to provide thermostatic switchmeans of the above type which is simple in construction, adapted forminiaturization, inexpensive to manufacture, and reliable in operation.

It is another object of the instant invention to provide a thermostaticswitch which is adapted for miniaturization so as to be convenientlyinsertable into the small spaces directly adjacent the'heated parts ofmotors, transformers, fluorescent ballasts and the like, to whichheating parts a temperature response is to be made by the switch.

It is yet another object of the instant invention to provide athermostatic switch means which is safe and reliable in operation and iseasily and simply calibrated.

It is also an object of the instant invention to provide simple,effective methods of accurately calibrating small thermostatic switches.

Among the several further objects of the instant invention may be notedthe provision of a thermostatic switch 3,361,883 Patented Jan. 2, 1968mum number of parts; and which is simple and economical to manufacture.

Other objects will be in ed out hereinafter.

The invention accordingly comprises the elements and combinations ofelements, steps and sequences of steps, features of construction andmanipulation, and arrangements of parts which will be exemplified in thestructures and methods hereinafter described, and the scope of theapplication of which will be indicated in the following claims.

In the accompanying drawings, in which several of the various possibleembodiments of the invention are illustrated;

FIG. 1 is a top plan view, partly in section of one embodiment of theinstant invention;

FIG. 2 is an elevational view of the switch shown in FIG. 1, with partsof the cover broken away;

FIG. 3 is a view taken on line 33 of FIG. 2;

FIG. 4 is a bottom plan view of a switch according to the instantinvention;

FIG. 5 is an enlarged detail sectional view taken on line 55 of FIG. 3;

FIGS. 6 and 7 are enlarged fragmentary views similar to FIG. 2 showingmethods of calibrating according to the instant invention.

Similar reference characters indicate corresponding parts throughout theseveral views of the drawings.

Dimensions of certain of the parts as shown in the drawings have beenmodified for the purposes of clarity of illustration.

Referring now to the drawings, and particularly to FIGS. 1-5, there isshown a thermostatic switch indicated generally by numeral 10.Thermostatic switch 10 comprises a thermostatic subassembly indicatedgenerally by numeral 12 and a tubular cover or container thereforindicated by numeral 14. Thermostatic subassembly 12 comprises a base 16including a projecting hub 18 and a peripherally extending flange 20,each of which are adapted to mate with the open end portion of containeror cover member 14, as best seen in FIGS. 1 and 2. Cover member 14 hasan inside peripheral configuration at its open end so as to provide asnug fit over the hub 18 and flush engagement with base 16, as shown in'FIGS. 1 and 2. Cover or container member 14 and base 16 are formed ofan electrically insulating moldable resin such as the phenolic resins orother thermosetting types.

As will be clear from the following description, thermally responsiveswitch 10 is both heat and current sensitive and is adapted to provideso-called inherent overheat protection. Thermostatic switch 10 includestwo electrically conducting terminals 22 and 24 extending through andprojecting on opposite sides of base member 16. As best seen in FIGS. 1and 2, terminal22, at its inner end, mounts an electrically conductingstationary contact 30, which is adapted to engage a movable contact 32carried by a thermostatic snap-acting disc 40. Disc 40 comprises arelatively thin, elongated thermostat metal strip which is dished ordeformed along substantially its entire length to provide for its snapaction. Deforming the disc along substantially its entire lengthprovides a snap-acting disc which is substantially free of creepmovement prior to snap movement of the disc. The use of such a disc inthe instant switch eliminates the need for additional specialcreep-inhibiting or preventing means.

Thermostatic switch 10 also includes an L-shaped mounting member or armhaving legs 44 and 46 arranged part apparent and in partpointsubstantially at right angles to each other. The free end of leg 46is embedded in base member 16 and does not extend through to theopposite side, as best seen in FIGS. 1 and 6. Base member 16 cantilevermounts the L-shaped mounting member and maintains the same inelectrically insulated relation to both terminals 22 and 24. Leg 44serves to cantilever mount thermostatic snap-acting disc 40, as bestseen in FIGS. 1, 2 and 4.

Leg 44 includes, along a portion of its length opposite the fixedcontact 30, a locating or centering recess 48 located in raised section50 on arm 44. One end of disc 40 is secured, as by welding to a weldingslug 54 of the type shown and described more fully in copendingapplication Ser. No. 291,202, filed on June 27, 1963, in the name ofMontague R. Duval and entitled, Means and Method for Making ElectricalConnections, and assigned to the assignee of the instant invention.

As is described more fully in the above-noted application, welding slug'54 includes a head portion 56 and a depending shank portion 58. Disc40, having a contact 32 welded thereto, is welded to head portion 56with shank portion 58 extending through aperture 52 in disc 40. In thismanner a disc assembly is formed which includes contact 32, disc 40 andslug 54. Thereafter slug 54 (and hence disc 40) is secured to arm 44 bya weld connection at recess 48 between arm 44 and the free end of shankportion 58. It will be noted that shoulders 59 on shank portion 58protects disc 40 from the effects of the welding at recess 48 as isdescribed in the Duval application. In this manner disc 40 is cantilevermounted on arm 44 and located such that contact 32 is movable into andout of engagement wtih stationary contact 30 in response to snapmovement of disc 40.

Electrically secured to a portion of leg 44 as by welding is one end ofan electrical heater 60 which may take the form of conventionalresistance heater wire or the like. Heater wire 60 may be provided withan electrically insulating coating. Although a round wire is illustratedas an example of a heating element, a planar heating element may also beused, and it is to be understood that this may be a strip, ribbon, orthe like, arranged in a plane. The term wire is used herein ascharacterizing each of these heater parts. Heater 60 is electricallyconnected as by welding at its other end to terminal 24. As best seen inFIG. 1, heater 60 is disposed below the snap-actine thermal element 40in close thermal juxtaposition therewith and is connected betweenterminal 24 and leg 44. It will be understood that heater 60 may takevarious forms and can be mounted in various ways between leg 44 andterminal 24 so as to be in close thermal juxtaposition to disc 40.

When contacts 30 and 32 are closed, as shown in FIG. 2, an electricallyconductive path is established leading from terminal 22, to contact 30,contact 32, through thermally responsive snap-acting disc 40, to leg 44,serially through heater 60, to electrically conducting terminal 24.

It will be understood that switch may be employed without heater 60 ifdesired.

In FIGS. 6 and 7 are shown methods of calibrating the switch 10.Referring to FIG. 6, during the assembly of thermostatic subassembly 12a disc assembly including a disc 40, contact 32 and slug 54 is selectedand located with the shank portion 58 in locating recess 48. Thereafterelectrodes 64 and 66 are located respectively on the upper surface ofhead portion 56 and on the under side of raised section 50. Thecompressive force between electrodes 64 and 66 retains the disc assemblyin fixed position on arm 44. It has been found that the temperature atwhich disc 40 will snap is a function of its location with respect tothe contact 30 and, more particularly, is a function of the angle xbetween the axial centerline b-b through slug 54 and the centerline a-athrough arm 46. By adjusting angle x the desired temperature setting orcalibration of the switch 10 can be achieved. A screw 68 or other meansfor applying a force to base 16 is located on the under side of base 16.Screw 68 is turned to apply a force tending to raise the base end of thesubassembly 12. Electrodes 64 and 66 retain the slug and arm in arelatively fixed position. However, as base 16 is raised from thesolid-line to the dotted-line position in FIG. 6, arm 44 is permitted topivot about the end P of shank 58, while slug 54 is retained in a fixedposition, centerline aa moves to a'a', thereby achieving the desiredangular relationship x and hence calibration. After the desired angle xis achieved, the assembly is welded at point P to preserve thecalibration. An alternate method of calibration is shown in FIG. 7.After the disc assembly has been welded to arm 44 to form subassembly12, the subassembly is located with a fixed support '70 located at theunder side of base 16 and a second support 72 located under a pointalong the length of arm 46. Thereafter a screw or other force applyingmeans is located along the length of arm 46 intermediate the base 16 andthe support 72 on the lower surface of arm 46. When screw 80 is turned aforce is brought to bear on the arm 46 tending to bend arm 46 from thesolid-line position to the dotted-line position shown in FIG. 7. Axialcenterline b-b through welding slug 54 moves to bb to form the axle xwhich is predetermined as the angle at which the desired calibration isachieved when screw 8'!) is released, arm 46 remains bent in thedotted-line position thereby preserving calibration.

It will be noted that the above calibration methods may be performedwith the subassembly and supports in various arrangements and in varyingorientations. It will also be understood that the bending of arm 46 andthe pivoting about point P may be in either direction as required.

It will also be understood that in ascertaining what the predeterminedcalibration should be, subassembly 12 may be located in an ambienttemperature equal to the desired snap open temperature and, thereafter,either of the above calibration methods may be followed until disc 40snaps open.

Terminals 22 and 24, and L-shaped mounting arm 46 may be cylindrical inform and may be formed of, for example, stainless steel. These elementsmay also be provided with knurled portions 22', 24 and 46 for connectionto base member 16. Thermostatic switch 10 may be quickly and easilyassembled. After the thermostatic subassembly 12 is prepared and thedisc 40 has been calibrated in the manner described above, thesubassembly 12 is slidably inserted into cover member 14, and securedthereto thereby sealing the device.

The complete calibrated and sealed device, in applications as a motorprotective device, may be inserted into a cavity in a small motor suchas a miniature motor currently in use in military aircraft, or thedevice can be buried in the windings of a motor that it is to protect.In such a place, it is responsive immediately and faithfully to theactual temperature of the motor winding. The terminals 22 and 24 are,for example, connected in series with one lead to the motor winding.Thus, if the motor should approach a temperature which is deleterious tothe winding insulation, or dangerous as a fire hazard, etc.,thermostatic element 4% will snap upwardly (as shown in the dashed linesin FIG. 2) to separate movable contact 32 from stationary contact 30,thus interrupting the current to the motor. When the motor has cooled toa predetermined temperature which is a preselected amount below the hotsnapping temperature, thermostatic element 40 will snap back to closethe circuit of the motor for re-energization thereof, Heater 6%), whichis in electrical series connection with thermostatic disc 40, may bedesigned so as to pass normal load currents but with abnormal currents,will generate suificient heat to quickly actuate the snap-acting disc 40to snap to a contacts-open position and interrupt the circuit.

From the above, it can be seen that the instant invention provides athermostatic switch which comprises a relatively small number of parts,which can be simply, quickly and inexpensively produced, and yet can besimply calibrated. The thermostatic switch comprises individualsubassemblies which can be mass produced and quickly and inexpensivelyassembled into operative position. The thermostatic switch of theinstant invention afliords a miniaturized construction with a relativelysmall number of parts.

The unique construction of the thermostatic switch of the instantinvention renders its operation substantial- 1y free from influence ofvibration and renders the thermostatic switch particularly suited toapplications where severe vibration is a factor.

The switch of the present invention has minimum heat mass and minimumsize, leading to quick heat response. Such quick heat responses are veryvaluable and are critical in certain motor protection applications.

Further, simplified accurate methods of calibration of the switch havebeen provided.

In view of the above it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

It is to be understood that the invention is not limited in itsapplication to the details of construction and arrangement of partsillustrated in the accompanying drawings, since the invention is capableof other embodiments and of being practised or carried out in variousways. Also, it is to be understood that the phraseology or terminologyemployed herein is for the purpose of description and not of limitation.

As many changes could be made in the above constructions and methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description or shown in theaccompanying drawings, shall be interpreted as illustrative and not in alimiting sense, and it is also intended that the appended claims shallcover all such equivalent variations as come within the true spirit andscope of the invention.

We claim:

1. A thermostatic switch adapted for miniaturization comprising a base;

first and second electrically-conductive terminals mounted on said basein electrically-insulated relation to each other;

a stationary contact provided by a portion of said first terminal;

a mounting arm having first and second intersecting portions, said firstarm portion being secured to said base in electrically-insulatedrelation to said first and second terminals, said second arm portionbeing disposed in spaced relation to said base and having a recesstherein forming a dish-shaped locating surface;

a snap-acting thermostatic member electrically-connected to said secondterminal and having a deformed portion responsible for its snap-action;

an electrical contact supported on one end of said thermostatic memberfor movement into and out of engagement with said stationary contact inresponse to snap movement of said thermostatic member; and

a welding lug secured to the opposite end of said thermostatic member,said lug having an end fitted within said mounting arm recess inselected angular relation to said mounting arm to engage said locatingsurface, said lug being welded to said mounting arm Within said recessfor supporting said thermostatic member in spaced, cantilever relationto said mounting arm in selected orientation relative to said stationarycontact for calibrating said switch.

2. A thermostatic switch as set forth in claim 1 wherein said weldinglug end has a rounded surface engageable with said locating surface in aplurality of angular orientations of said lug relative to said mountingarm.

3. A thermostatic switch as set forth in claim 2 wherein said deformedportion of said thermostatic member extends along substantially theentire length of said thermostatic member to substantially limitmovement of said thermostatic member to snap movement thereof.

4. A thermostatic switch as set forth in claim 2 Wherein saidthermostatic member is electrically connected to said second terminal bymeans of electrical heater means disposed in thermal juxtaposition tosaid thermostatic member.

5. The method of calibrating a thermostatic electrical switch comprisingthe steps of mounting a stationary contact on a base, mounting an arm onsaid base so that an arm recess forming a dish-shaped locating surfaceis disposed in spaced relation to said stationary contact, attaching awelding lug to one end of snap-acting thermostatic member so that oneend of said lug extends from said member, holding said lug end inengagement with said locating surface on said arm, orientating said lugin selected angular relation to said arm while in engagement with saidlocating surface to position said thermostatic member in selectedorientation relative to said stationary contact, and welding said lug tosaid arm in said selected angular relation to said arm for calibratingsaid switch.

6. A method of calibrating a thermostatic electrical switch as set forthin claim 4 wherein said lug end is held in engagement with said locatingsurface by gripping said lug end arm between electrodes and wherein saidlug is welded to said arm by passing electrical current between saidelectrodes through said lug end arm.

References Cited UNITED STATES PATENTS 1,968,976 8/1934 Van Halteren219-93 2,564,931 8/1951 Smith ZOO-138.3 2,740,034 9/ 1956 Carlyle 219-932,800,555 7/1957 Sundt ZOO-122.03 3,004,203 10/1961 Epstein ZOO-122.033,064,100 11/1962 Malone ZOO-113.7 3,148,256 9/1964 Perry 200-1223,171,925 3/1965 Malone et al. ZOO-113.6 3,194,924 7/1965 Moksu et al.200-122 3,280,285 10/1966 Audette ZOO-113.7 3,288,967 11/1966 PerryZOO-138.3 X 3,299,239 1/1967 Mawney 200-113 X OTHER REFERENCES Reich:The Welding Journal, 1946, pp. 1189-1192.

BERNARD A. GILHEANY, Primary Examiner.

H. A. LEWITTER, Assistant Examiner.

